The output of an MPEG Audio or Video Encoder is called an elementary stream. An elementary stream is a compressed representation of the audio or video source and may be broken into data blocks of manageable size, forming a packetized elementary stream (PES). The data blocks, known as PES packets, include PES header information to identify the start of the packets. Additionally, the packets also include time stamps, known as presentation time stamps (PTS), and decode time stamps (DTS) because packetizing can disrupt synchronization.
For transmission and digital broadcasting, several programs and their associated PES can be multiplexed into a single transport stream. The transport stream differs from a program stream in that the ES packets are further subdivided into short fixed-size packets of 188 bytes. Additionally, transport streams can carry multiple programs encoded with different clocks. The transport stream comprises fixed size data packets containing 188 bytes.
While the PES stream is packetized into 188 byte transport packets, PES packets do not have a fixed length. PES headers can start anywhere and any number of times with a 188-byte transport packet. Additionally, PES headers can also straddle across 188-byte transport packet boundaries. The foregoing makes PES header detection complex.
Some systems implement PES header detection in firmware. Implementation of PES header detection in firmware consumes significant processor bandwidth, thus limiting the bit rate handling capability of the video transport processor.
Alternatively, PES header detection can be handled in hardware. However, PES header detection in hardware is unable to detect PES headers that straddle transport packets. Accordingly, detection of PES headers that straddle transport packets is still handled in firmware.
Further limitations and disadvantages of convention and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings.